JP6025230B2 - Inverse opal structure metal catalyst electrode for fuel cell and manufacturing method thereof - Google Patents

Description

  The present invention relates to a metal catalyst electrode having an inverse opal structure used as a catalyst layer included in a membrane / electrode assembly (MEA) of a fuel cell, and a method for producing the same.

  Hydrogen is the most abundant element on earth and can be converted to new renewable energy without emitting greenhouse gases and pollutants. In particular, when hydrogen is used as a fuel for a fuel cell that directly converts chemical energy generated by a chemical reaction between reactants into electrical energy, it exhibits excellent efficiency corresponding to about 2.5 times that of an internal combustion engine. Therefore, fuel cells using hydrogen are attracting much attention as a promising future technology for energy conversion.

  Such fuel cells may be polymer electrolyte fuel cells (PEMFC), alkaline fuel cells (AFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid oxides depending on the type of electrolyte used. It is divided into fuel cells (SOFC). In particular, polymer electrolyte fuel cells have a relatively low operating temperature, can be miniaturized, have a high energy density, and can use hydrogen or methanol as a fuel. It can be flexible in size and combination when done, and is considered the closest to commercialization.

  In a polymer electrolyte fuel cell, a membrane / electrode assembly (MEA), which is a core component that determines the performance of a fuel cell, is composed of a catalyst serving as an electrode and a membrane serving as an electrolyte. Although it has a unitary structure, it mainly uses expensive platinum (Pt) particles as the catalyst, and this acts as the biggest obstacle to the commercialization of fuel cells.

  Therefore, there is an urgent need to minimize the amount of platinum used by improving mass transfer and improving water management through a meticulous design of the electrode structure.

  In this connection, electrodes using carbon-based nanomaterials such as conventional carbon nanotubes as a support for platinum catalyst particles are known (Non-Patent Documents 1 to 3). For obtained by high difficulty and high cost manufacturing process. In addition, corrosion and oxidation of the carbon support occurs in accordance with the operation of the fuel cell, and there is a concern about a decrease in durability, and the platinum catalyst particles disappear in the catalyst layer because it is manufactured based on a solution process. Has a problem.

  As an alternative to solve the above-described problems of the conventional electrode, a platinum catalyst electrode having an inverse opal (IO) structure can be considered.

  Here, the inverted opal structure is a structure in which small nano-unit structures are periodically repeated, and the length of the spatial structure arranged in this way roughly corresponds to the wavelength of visible light. It means a structure made by forming pores in the opal structure, which is a crystal structure that shows various colors.

  Such an inverse opal structure is composed of open pores that are three-dimensionally aligned and interconnected, so that it is expected that improved mass transfer and effective water management are possible. Nevertheless, it is difficult to find a case where the inverse opal structure is applied as an electrode to a fuel cell, particularly a polymer electrolyte fuel cell. This is because the process is very troublesome in the production of a membrane / electrode assembly provided with a catalyst layer having an inverse opal structure.

  Specifically, in the fabrication of inverted opal structures, a commonly used colloidal template method uses a glass slide, silicon wafer, ITO (indium tin) as a support for self-assembly of colloidal particles. gas diffusion layer (Gas Diffusion Layer) having a rough, non-uniform, and chemically heterogeneous surface in order to require a substrate having a smooth and uniform surface, such as Oxide) and FTO (fluorine-doped tin oxide). It is practically impossible to directly form a catalyst layer having an inverse opal structure on the GDL), and a process for transferring the catalyst layer having an inverse opal structure to a gas diffusion layer must be further performed. This is because it seemed.

Chai, GS, Shin, IS & Yu, J.-S.Synthesis of ordered, uniform, macroporous carbons with mesoporous walls templated by aggregates of polystyrene spheres and silica particles for use as catalyst supports in direct methanol fuel cells.Adv. Mater. 16, 2057-2061 (2004) Wang, C. et al. Proton exchange membrane fuel cells with carbon nanotubebased electrodes.Nano Lett. 4, 345-348 (2004) Yuan, F. L. & Ryu, H. J. The synthesis, characterization, and performance of carbon nanotubes and carbon nanofibres with controlled size and morphologyas a catalyst support material for a polymer electrolyte membrane fuel cell.Nanotechnology 15, S596-S602 (2004)

  The object of the present invention is that it has an inverted opal structure that can improve the mass transfer and increase the efficiency of water management in the fuel cell due to its structural advantages, has durability, and can be directly formed on the gas diffusion layer. An object of the present invention is to provide a metal catalyst electrode for a fuel cell and a method for producing the same.

  In order to achieve the above object, the present invention provides a metal catalyst electrode having an inverse opal structure for a fuel cell.

  The present invention also includes (a) a step of pretreating the surface of the gas diffusion layer (GDL), (b) a step of forming a template on the gas diffusion layer, and (c) a metal precursor solution on the template. A method for producing a metal catalyst electrode having an inverted opal structure for a fuel cell, comprising: forming a metal skeleton after impregnating the substrate; and (d) removing the template.

  The metal catalyst electrode having an inverse opal structure for a fuel cell according to the present invention minimizes the concentration loss, and has a high effective porosity and effective catalyst utilization by an open pore structure that is three-dimensionally aligned and interconnected. In addition, it is possible to realize a fuel cell with significantly improved performance by enabling mass transfer and efficient water management. In particular, based on the dramatically improved power density and water management capability, it is possible to realize an actual unit cell with further improved performance while reducing the amount of platinum used compared to existing fuel cells. As a result, since the metal catalyst electrode according to the present invention is composed of only the catalyst metal, the corrosion problem of the electrode and the disappearance of the metal catalyst are lost as compared with the catalyst electrode including the metal catalyst supported by the existing carbon material or the carbon-based support. There is no risk of occurrence.

  The method for producing a metal catalyst electrode having an inverse opal structure for a fuel cell according to the present invention is a method for producing a metal catalyst electrode having an inverse opal structure included in a membrane / electrode assembly of a fuel cell. A metal catalyst electrode having an inverted opal structure having excellent performance as described above can be easily and economically produced without a troublesome process of transferring the catalyst electrode to a gas diffusion layer after it is separately manufactured.

1 (a) and 1 (b) show a conventional membrane / electrode assembly for a fuel cell (MEA) and a membrane / electrode assembly including a metal catalyst electrode having an inverted opal structure for a fuel cell according to the present invention. FIG. 3 is a flowchart showing each stage of a method of manufacturing a metal catalyst electrode having an inverse opal structure for a fuel cell according to the present invention. It is a conceptual diagram which shows each step of the manufacturing method of the metal catalyst electrode which has the reverse opal structure for fuel cells which concerns on this invention, and a field emission type | mold scanning electron microscope (FE-SEM) image with respect to the structure obtained at a relevant step. Field-emission scanning electrons showing that the microstructure of the inverse opal structure changes due to changes in duty cycle, pulse application / interruption time (on / off time), and current density (current density) during pulse electrodeposition It is a microscope (FE-SEM) image. FIGS. 5 (a) and 5 (b) each show a structure of a single cell manufactured including a membrane / electrode assembly (MEA) having an inverted-opal structure electrode manufactured in an embodiment of the present invention. It is a field emission type | mold scanning electron microscope (FE-SEM) image which shows the cross section of the film | membrane / electrode assembly containing the platinum electrode of the reverse opal structure manufactured in the Example of this invention, and each layer, and the partial expansion degree of each layer. 3 is an X-ray diffraction analysis (XRD) result for an electrode having an inverse opal structure manufactured in an example of the present invention. FIGS. 7A and 7B are X-ray photoelectron spectrum (XPS) analysis results for the existing Pt / C electrode and the platinum electrode of the inverse opal structure manufactured in the example of the present invention, respectively. It is a graph which shows the distribution of a platinum oxidation state in each of the existing Pt / C electrode and the platinum electrode of the inverse opal structure manufactured in the Example of this invention. 4 is a polarization curve and a power density curve according to the operating conditions of a fuel cell unit cell with respect to a platinum electrode-based membrane / electrode assembly having a reverse opal structure according to the present invention and a conventional membrane / electrode assembly. .

  Hereinafter, the present invention will be described in detail.

  The metal catalyst electrode according to the present invention has an inverse opal (IO) structure, and is a membrane / electrode assembly in a fuel cell, in particular, a polymer electrolyte fuel cell (PEMFC). ).

  The metal catalyst electrode may be directly formed on a gas diffusion layer (GDL).

  Conventionally, there has been no method capable of directly forming an inverted opal structure on a substrate having a rough and non-uniform surface, such as a gas diffusion layer made of carbon paper made of carbon fiber. Therefore, in order to laminate a photonic crystal having an inverse opal structure on a substrate having a rough and non-uniform surface, a glass slide, a silicon wafer, an ITO (indium tin oxide) substrate, an FTO (fluorine-doped oxide) ) After forming a layer of an inverse opal structure on a substrate having a smooth and uniform surface such as a substrate, a process of transferring the layer onto a substrate having a rough and uneven surface must be further performed. Therefore, the process is very troublesome and uneconomical.

  On the other hand, the metal catalyst electrode having an inverse opal structure according to the present invention is characterized in that it is directly formed on the gas diffusion layer (GDL) without performing another transfer process.

  The metal catalyst electrode according to the present invention has a merit peculiar to the inverse opal structure in which the macropores are three-dimensionally and regularly arranged. That is, since the metal catalyst electrode according to the present invention has a high specific surface area, a low degree of flexibility, and interconnected pores, the membrane / electrode assembly of a fuel cell, particularly a polymer electrolyte fuel cell. When introduced as a catalyst layer in (MEA), improved mass transfer and efficient water management compared to existing catalyst layers such as platinum catalyst layers with carbon-based supports can do.

  More specifically, firstly, the metal catalyst electrode according to the present invention is very open and has a diffusion path having a low degree of bending compared to the bent structure of the conventional metal catalyst layer, so that mass transport and conductivity are achieved. Promote improvement. In addition, since it has a larger interfacial area where electrode reaction can occur, the reaction rate is improved. Further, by allowing the thickness of the catalyst layer to be reduced, unlike existing catalyst layers, it is not necessary to include an ionomer. In addition, since the metal catalyst particles have an integrated structure in which the entire inverse opal structure is bound, loss of the metal catalyst particles can be prevented.

  In an electrode having a disordered structure such as a membrane / electrode assembly (FIG. 1 (a)), which is manufactured by an existing CCM (Catalyst Coated Membrane) method and includes a catalyst layer including a platinum catalyst supported by a carbon support, Since the movement of molecules tends to be hindered by pore walls and other particles, a membrane / electrode assembly having a catalyst electrode having an inverse opal structure like the metal catalyst electrode according to the present invention (FIG. 1B) ) Shows a significantly lower mass diffusivity.

  On the other hand, the metal catalyst electrode according to the present invention exhibits a further improved mass diffusivity due to the open pores and the interconnected pore structure, thereby making it possible to produce thinner electrodes.

  On the other hand, the metal catalyst electrode having an inverted opal structure according to the present invention is not only platinum (Pt) mainly used as a material forming a catalyst layer in a membrane / electrode assembly of a fuel cell, but also ruthenium (Ru), rhodium (Rh). ), Palladium (Pd), another platinum group metal such as osmium (Os) or iridium (Ir), or one or more of the platinum group metals and iron (Fe), cobalt (Co) or nickel (Ni) It may be made of an alloy.

  Hereinafter, the manufacturing method of the metal catalyst electrode of the reverse opal structure for fuel cells which concerns on this invention is demonstrated.

  As shown in FIG. 2, the method for manufacturing a metal catalyst electrode having an inverse opal structure for a fuel cell according to the present invention includes: (a) pre-treating the surface of the gas diffusion layer (GDL); b) forming a template on the gas diffusion layer; (c) impregnating the template with a metal precursor solution and then forming a metal skeleton; and (d) removing the template. And comprising steps. Next, the steps (a) to (d) will be described in detail.

  The step (a) is a preliminary step for directly forming a metal catalyst electrode having an inverse opal structure on the gas diffusion layer, and is a template serving as a template for forming the gas diffusion layer and the inverse opal structure described later. In order to improve the adhesion between the two, the surface of the gas diffusion layer is pretreated.

  Specifically, in this stage, before forming the template on the gas diffusion layer, a linker is introduced on the surface of the gas diffusion layer in order to improve the adhesion between the gas diffusion layer and the template.

  For example, as in the embodiments of the present invention to be described later, on a gas diffusion layer made of carbon black having thiol groups on the surface using spherical polystyrene (PS) colloidal particles functionalized with carboxyl groups. When a template is formed on the substrate, a gas serving as a substrate in a solution in which a surface modifying compound such as 1,2-ethanedithiol is dissolved in order to introduce alkanethiol as a linker to the surface of the gas diffusion layer. This step can be performed by immersing the diffusion layer.

  In the step (b), a template which is a template for forming a metal catalyst electrode having an inverse opal structure is formed on the surface-treated gas diffusion layer.

  A specific method for performing this step, or a material of a template to be formed is not particularly limited, but preferably, crystallization using capillary force, crystallization by precipitation using gravity, Alternatively, colloidal crystals in which spherical polymer colloidal particles are three-dimensionally aligned can be produced by crystallization using electrostatic repulsion of particles having surface charge.

  At this time, the spherical polymer colloidal particles contained in the solution in which the colloidal particles are dispersed are strongly bonded to the gas diffusion layer by the linker introduced into the gas diffusion layer through the surface treatment of the step (a), and self-assembly ( A template made of colloidal crystals is formed by self-assembly).

  3 (a) and 3 (b) are conceptual diagrams showing a process of obtaining a three-dimensional aligned colloidal crystal template by capillary force using a suspension in which spherical polymer colloidal particles are dispersed, and are obtained thereby. A schematic diagram of a colloidal crystal template and a field emission scanning electron microscope (FE-SEM) image are shown.

  According to FIGS. 3 (a) and 3 (b), at this stage, when the water in the suspension containing polymer colloidal particles such as spherical polystyrene (PS) particles evaporates from the meniscus, Molecular colloidal particles are continuously transported near the triple-phase contact line by the convective fluid flow of the surrounding suspension, and at the same time, the capillary force is increased while the film is dry. The polymer colloidal particles are pulled to form an ordered dense colloidal crystal template.

  On the other hand, the type of the polymer colloidal particles is not particularly limited. Polystyrene, polymethylmethacrylate, polyacrylate, polyalphamethylstyrene, polybenzylmethacrylate, polybenzylmethacrylate, polymethylmethacrylate, polyacrylate, polyalphamethylstyrene, polybenzylmethacrylate. (Polybenzyl methacrylate), polyphenyl methacrylate, polydiphenyl methacrylate, polycyclohexyl methacrylate, styrene-acrylonitrile copolymer, styrene-acrylonitrile crylonitrile copolymer), or styrene - methyl methacrylate copolymer (styrene-methacrylate copolymer) may be made from such.

  In addition, the polymer colloidal suspension may further include a nonionic surfactant to promote self-assembly and crystallization of the polymer colloid particles through changes in hydrophilicity and surface tension. it can.

  At this stage, as the evaporation rate and concentration of the colloidal suspension increases, a thicker template can be obtained, so that the desired template thickness can be achieved by changing the solvent evaporation rate or solution concentration.

  The step (c) is a step of forming a metal skeleton after impregnating the metal precursor solution into the template, specifically, inside the template formed of the colloidal crystal formed in the step (b). After impregnating the precursor of the desired metal or alloy, using electrochemical deposition method, sol-gel method, precipitation method, oxide reduction method, solvent thermal synthesis method, CVD method, electroless plating method, thermal decomposition method, etc. A metal skeleton is formed.

  Among the various methods mentioned above as the method for forming the metal skeleton, the electrochemical vapor deposition method is satisfied even if any material that forms the metal skeleton grows in the interstitial space in the template and there are any cracks. Since it has the advantage that the space can be almost completely filled, the shrinkage hardly occurs after the removal of the template, and the mechanical strength is increased. When using pulsed electrodeposition (Galvanostatic-pulsed deposition), the physical properties of the deposit and the adhesion to the substrate are improved, and the nucleation and crystal growth of the metal are individually controlled by adjusting the pulse amplitude and deposition time. Together with the additional advantage of being able to control automatically.

  Next, the step (d) is a step of removing the template in order to leave only the metal catalyst skeleton having an inverse opal structure, and there is no particular limitation on a specific method for performing the step. For example, the template can be removed by dissolving the template using an organic solvent such as toluene or acetone, or by calcining the template at a low temperature.

  Next, the present invention will be described in detail based on examples. These examples are illustrative only and are not intended to limit the scope of the invention.

<Example: Production of platinum electrode with inverted opal structure>
1. And 2. Then, a platinum electrode having an inverse opal structure according to the present invention was manufactured.

[1. Production of Opal Polystyrene (PS) Template]
Prepared as a substrate is a gas diffusion layer (GDL) (35BC, SGL) containing MPL (Microporous layer) that has been surface-treated by immersing it in an ethanol solution (10 mM) in which 1,2-ethanedithiol is dissolved for 12 hours or more. did. For reference, the MPL comprises carbon black and 5% by weight of polytetrafluoroethylene, and the alkanethiol introduced to the surface of the gas diffusion layer by the surface treatment includes the carboxyl group on the polystyrene particle surface and the MPL. It acts as a kind of binder or coupling agent by interacting with the terminal thiol group on the surface of carbon black contained in.

  Meanwhile, after mixing 0.36 g of 0.5 wt% nonionic surfactant (IGEPAL Co-30) and 80 mL of Milli-Q water, this was mixed with carboxyl functionalized polystyrene (Carboxylated PS) latex particles (average A polystyrene colloidal suspension for template production was prepared by adding to 0.5 g of a 10% by weight aqueous suspension in which the particle size was 520 nm).

  Next, as shown in FIG. 3A, the substrate was immersed in the polystyrene suspension and then wetted. Then, after ultrasonic treatment for 30 minutes, the polystyrene template having an opal structure was formed on the gas diffusion layer by drying in a 65 ° C. oven at a constant relative humidity for 2 days or more.

[2. Production of platinum (Pt) electrode with inverted opal structure]
In a plating bath containing 10 mM H ₂ PtCl ₄ solution dissolved in 10 mM KCl, constant current-pulse electrodeposition (using a three-electrode cell with a platinum plate and Ag / AgCl as a counter electrode and a reference electrode, respectively) Platinum was vapor-deposited on the surface and inside of the polystyrene template by performing Galvanostatic-pulsed electrodeposition. During the deposition, the gas diffusion layer located under the polystyrene template served as the working electrode.

  After completion of the deposition, the substrate on which platinum was deposited was immersed in toluene for 12 hours to remove polystyrene particles. Thereafter, the substrate was taken out of the solution and washed with water, and then heated in an air atmosphere and 130 ° C. for 4 hours in order to remove water and contaminants remaining in the space in the electrode. Thereafter, as an optional step, heat treatment was performed in a hydrogen atmosphere and 180 ° C. for 2 hours to remove the remaining organic solvent and minimize platinum oxidation.

  FIG. 4 shows field emission showing that the microstructure of the inverse opal structure changes due to changes in duty cycle, pulse application / interruption time (on / off time), and current density (current density) during pulse electrodeposition. It is a type | mold scanning electron microscope (FE-SEM) image.

In order to obtain an electrode surface having a better shape, the current density, duty cycle and charge density were varied. On the other hand, the total charge density was fixed at 4 Ccm ⁻² corresponding to a theoretical platinum loading of 0.2 mgcm ⁻² . However, as a result of measurement using an inductively coupled plasma (ICP) mass spectrometer, the content of platinum deposited on the gas diffusion layer was 0.12 mgcm ⁻² . And the thickness of each reverse opal structure electrode was about 1-2 micrometers (refer FIG.5 (b)). Thus, a total charge of 1 Ccm ⁻² was deposited. This corresponds to a platinum deposition of 0.03 mg cm ⁻² and a thickness of about 0.5 μm. The polystyrene spherical particles were deposited as 5 to 20 layers on the gas diffusion layer, and the corresponding thickness was about 3 to 12 μm. In the case of a platinum sphere having an inverted opal structure, the thickness was about 3 to 4 layers (1.5 to 2 μm). The thickness was determined taking into account the limited amount of platinum, the conserved inverse opal structure and smooth proton transport. Considering that the typical thickness of conventional electrodes in polymer electrolyte fuel cells is about 5-10 μm, the inverse opal platinum electrode has a shorter diffusion path and increased conductivity of reactants and ions. Because it has, it is superior to existing electrodes. This means that the use of ionomers for proton transport is unnecessary.

  Moreover, the thickness of the platinum wall was about 10-15 micrometers. This was obtained by roughly calculating the ratio of the scanning electron microscope (SEM) image to the surface.

  On the other hand, in the case of a template having an opal structure, the skeleton wall includes macro pores interconnected through holes at a point where the original polystyrene spherical particles contact. In fact, the structure of the inverse opal material obtained from electrodeposition by the colloidal crystal template method is generally formed to fill the interstitial space of the template with the desired material. However, such a phenomenon was not observed from the platinum electrode having the inverse opal structure manufactured in this example. Instead, platinum surrounded the polystyrene spherical particles making a shell (see FIG. 1 (b) and FIG. 3 (d)).

  As a result of performing X-ray diffraction analysis (XRD) in order to confirm whether a platinum component is present on an electrode having an inverse opal structure, 40.06 °, 46.54 ° in the corresponding XRD spectrum shown in FIG. And three major peaks appearing at 67.86 ° correspond to the (111), (200) and (220) planes of platinum, respectively. The characteristic peak appearing at about 27 ° is generated by carbon contained in the MPL of the gas diffusion layer. The size of the platinum particles formed on the electrode-based membrane / electrode assembly having an inverse opal structure was calculated to be about 8 to 11 nm using the Scherrer equation and X-ray diffraction data.

  In addition, as a result of obtaining and analyzing X-ray photoelectron spectrum (XPS) in order to confirm the oxidation state of platinum in the electrode of the reverse opal structure, the oxidation state of platinum in the electrode of the reverse opal structure is the same as that of the existing Pt / C electrode. Could be confirmed to be very different. That is, the corresponding spectrum shown in FIG. 7 is derived from an existing Pt / C electrode, and the 4f core level peak of platinum is mainly derived from Pt (0) (see FIG. 7 (a)), but has an inverse opal structure. In the case of a platinum electrode, the main peak is derived from Pt (II) (see FIG. 7B). In addition, the distribution of the platinum oxidation state in the IO electrode is different from Pt / C in the existing electrode (see FIG. 8). However, since the oxidation state of the platinum surface is sensitive to heat treatment conditions and easily changes during cell operation, such results are not significantly related to cell performance.

<Experimental Example: Performance Test for Membrane / Electrode Assembly (MEA) Containing Inverse Opal Structure Electrode Produced in Example of the Present Invention>
As described below, a membrane / electrode assembly (MEA) was manufactured using the inverted-opal structure electrode manufactured in the above example, and then a single cell including the same was manufactured.

That is, an electrode having an inverted opal structure manufactured by performing pulse electrodeposition under specific conditions (peak current density: 50 mAcm ⁻² , on / off time: 50/100 ms, total charge: 4 Ccm ⁻² ) in the above-described embodiment. Used as the cathode and 40 wt% Pt / C was used as the anode catalyst. At this time, the Pt / C catalyst was dispersed in a mixture of isopropyl alcohol, deionized water and perfluorosulfonic acid ionomer, and then the ion conductive membrane (Nafion 212, 0.25 mg Pt · cm ⁻² ). DuPont) was applied by spraying to the anode side. Thereafter, a gas diffusion layer (35BC carbon paper, SGL) was disposed on the anode side. The membrane / electrode assembly manufactured in this way was inserted into a single cell unit provided with a graphite plate having an area of 5 cm ² and provided with a serpentine gas flow channel (FIG. 5). (See (a)).

The activation and polarization tests of the single cell assembled as described above were performed by a current-sweep-hold method using a fuel cell test system (CNL Energy). Specifically, the current-sweep rate was 10 mAcm ⁻² S ⁻¹ . When the current density reached 0.5, 1.0, 1.5, 2.0, 2.5, ³ , and 4 Acm ² , the current was maintained for 10 minutes. When the cell voltage reached 0.35 V during activation, the current was reset to 0.

Polarization curves were obtained using a current-sweep method and a polymer electrolyte fuel cell (PEMFC) test system. Activation and polarization tests were performed using fully humidified H ₂ / O ₂ (or air). The anode stoichiometry, the cathode stoichiometry for O ₂ and the air stoichiometry are 2, 9.5 and 2, respectively, and the total outlet pressure is the total outlet pressure. It was 150 kPa. The cell temperature was maintained at 80 ° C. during the activation test and at room temperature during the polarization test. In the case of cathodic dead-end mode, the O ₂ flow rate was minimized and the cell outlet was closed.

FIG. 9 shows a polarization curve and a power density curve for a platinum electrode-based membrane / electrode assembly having an inverse opal structure according to the present invention and a conventional membrane / electrode assembly. FIG. 9 (a) and FIG. 9 (b) show a platinum loading of about 0.12 mg Pt · cm ⁻² with H ₂ / O ₂ fully humidified at 70 ° C. by cathode dead-end mode, respectively, and FIG. 9 (c) and FIG. 9 (d) are the results when the platinum loading is about 0.12 mg Pt · cm ⁻² using H ₂ / O ₂ at ambient temperature and ambient humidity. US Department of Energy's when by reference) using a _H 2 / Air was completely moistened with 80 ° C. by standard fuel cell test conditions, the platinum low computing each 0.12mgPt · ^{cm -2} and 0.12mgPt · ^{cm -2} The result is shown.

  From FIG. 9, the membrane / electrode assembly (MEA) based on the inverse opal structure electrode in the polymer electrolyte fuel cell (PEMFC) has a morphological advantage unique to the inverse opal structure, an interconnected pore structure, and an open electrode. It can be seen that the improved effective diffusivity from the surface shows higher performance than existing membrane / electrode assemblies with similar platinum loading.

For example, in the case of an existing membrane / electrode assembly, the current density at 0.6 V was 235 mAcm ⁻² , but the inverse opal structure electrode substrate membrane / electrode junction according to the present invention having a platinum loading similar to the above is used. The current density measured under the same conditions for the body was 440 mAcm ² , indicating a value that was significantly increased by about 185% (see FIG. 9A). Moreover, the performance of the inverted opal structure electrode substrate according to the present invention was even better when the measurement was performed under standard conditions at H ₂ / air (see FIG. 9 (c) and FIG. 9 (d)). .

  In particular, the difference becomes even more pronounced when platinum loading is higher and thicker electrodes are used (see FIG. 9 (d)). This is because, although the concentration loss due to the transfer of reactants and products increases in the thicker electrode, the increase width is larger when the existing membrane / electrode assembly is used.

  Specifically, in the case of a thicker electrode, the reactant must diffuse a greater distance in order to reach the catalyst layer where the reaction takes place. Similarly, thicker electrodes need to diffuse a greater distance in order for the product to be removed from the fuel cell.

  On the other hand, in the insets in FIGS. 9 (a) to 9 (d), the power density difference between the membrane / electrode assemblies on both sides becomes significant when the voltage is 0.7V or less, but is 0.7V or more. Not noticeable with voltage. This is because a potential of 0.7 V or more exists in the charge transfer-controlled region.

  Therefore, the performance of the polymer electrolyte fuel cell in the low-current region is almost the same in the unit cells on both sides, but in the high-current region, in the case of the unit cell including the inverted opal structure electrode, Because depletion is reduced by the morphological advantages of inverted opal structures (e.g., easy accessibility of materials with relatively large surface area, very open and low flex structures, and interconnected macropores), A unit cell including an electrode having an inverse opal structure exhibits a higher power density.

  In addition, the electrochemical surface area (ECSA) of the platinum catalyst is measured by the cyclic voltage current method (CV) using a constant voltage / galvanostat (IM-6, Zahner). did.

  The measurement of electrochemical characteristics was performed using standard inverted opal platinum electrodes, platinum plates and saturated calomel electrodes prepared in the above examples as working electrodes, counter electrodes, and reference electrodes, respectively. A three-compartment electrochemical cell was used using a voltage regulator (PGSTAT128N, Autolab). All potentials were based on the potential of a standard hydrogen electrode (NHE), and all measurements were performed at room temperature.

In the inverse opal-structured platinum electrode-based membrane / electrode assembly and the conventional membrane / electrode assembly according to the present invention, the electrochemical surface area (ECSA) of the platinum catalyst is a constant voltage / constant current device ( It was measured by the cyclic voltage current method (CV) using IM-6, Zahner. As a result, the electrochemical surface area of the platinum electrode-based membrane / electrode assembly having an inverse opal structure is 24.13 m ² g ⁻¹ and the geometric surface area (GSA) is 40.04 m ² g. Measured to be ^-1 . This shows that the platinum utilization (ECSA / GSA) is about 60.27%. On the other hand, the electrochemical surface area of the existing membrane / electrode assembly is 57.01m ² g ^-1, geometric surface area is ^93m 2 ^{g -1,} platinum utilization degree was measured to be about 61% It was.

  According to the above results, the GSA and ECSA of the existing membrane / electrode assembly were measured higher than the membrane / electrode assembly of the inverted opal electrode base, but the higher ECSA was always better in actual fuel cell operating conditions. Does not show performance. Moreover, the concepts of GSA, ECSA and platinum utilization (ECSA / GSA) only describe hydrogen adsorption / desorption reactions related to catalytic capacity, gas diffusion in membrane / electrode assemblies, ion conduction pathways It does not include overall process parameters such as proton conductivity, water and mass transfer. In addition, the platinum utilization level does not include a kinetic parameter. That is, this suggests that the inverse opal electrode-based membrane / electrode assembly can exhibit further improved performance even when it has substantially the same platinum utilization as the existing membrane / electrode assembly.

  Fuel cell loss can be divided into three categories: activation loss, resistance loss and concentration loss (or mass transfer loss). Among these, the mass transfer loss occurs over the entire current density range, but is particularly noticeable in a high limiting current region, that is, a low potential region. Therefore, polarization in the high current density region indicates mass transfer loss.

  Inverse opal electrodes consist of interconnected and open pore spaces with increased effective porosity and reduced diffusion layer thickness compared to existing electrodes, resulting in significant mass transfer And thus such improved mass transfer can lead to superior water management. This superior water management capability promotes back diffusion when water is insufficient, that is, the phenomenon that the generated water diffuses from the cathode to the anode through the separation membrane due to the water concentration gradient. Cell performance can be prevented from decreasing.

The effects as described above can be confirmed from FIG. According to FIG. 9 (b), the current density measured at 0.6V (high current density region) with respect to the existing membrane / electrode assembly under normal temperature and ambient humidity is 666 and is 367 mAcm ⁻² abruptly. However, in the case of a membrane / electrode assembly based on an inverted opal structure electrode, it decreased to 495 mAcm ^{-2 at} 790, a 37% decrease. In other words, the membrane / electrode assembly based on the reverse opal structure electrode has a very open structure with a low degree of bending and a short diffusion path, so that it has better water transport capability, so that the cell performance deteriorates even in low humidity conditions. It is understood that is not large.

  In addition, reactants and products are transmitted primarily through macro-sized secondary pores rather than meso-unit pores, and the mass transfer of membrane / electrode assemblies in single cells is this. It is governed by such secondary processing. Therefore, an inverted opal structure electrode having an aligned macroporous structure can actually achieve better performance and more efficient water management in a fuel cell device.

  As mentioned above, reverse-opal electrode-based membrane / electrode assemblies perform better than existing membrane / electrode assemblies, especially in the periphery due to improved mass transfer and better water management Such performance excellence is significant in humidity conditions and high current regions.

  Further, the open circuit voltage (Open Circuit Voltage, OCV) of the existing membrane / electrode assembly is 0.935 V at ambient humidity and room temperature, but the open circuit of the reverse opal electrode-based membrane / electrode assembly according to the present invention. The voltage is 0.982V. Such a difference suggests that the mixed cathode potential associated with the reaction between platinum surface and oxygen or the oxidation of impurities at the inverse opal structure electrode is lower than that of the existing membrane / electrode assembly.

  Therefore, it can be seen that the electrode of the inverse opal structure according to the present invention can be directly applied as the electrode of the membrane / electrode assembly in the polymer electrolyte fuel cell. And more importantly, the inverse opal electrode requires very low platinum rotting, and its performance is a direct direct methanol fuel cell (Direct Methanol Fuel Cell) under operating conditions with similar ambient humidity and heating. , DMFC). Further, unlike other fuel cell systems, a fuel cell equipped with an inverse opal electrode does not require any complicated subsystem or BOP (Balance of Plant), and therefore is promising for application to a micro fuel cell.

Claims (5)

(A) pre-treating the surface of the gas diffusion layer in order to improve adhesion between the gas diffusion layer (Gas Diffusion Layer, GDL) and the template ;
(B) forming a template on the gas diffusion layer;
(C) After the metal precursor solution is infiltrated into the template, it is selected from the group consisting of platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os) and iridium (Ir). (Ii) forming a metal skeleton composed of an alloy of one or more of the platinum group metals and iron (Fe), cobalt (Co), or nickel (Ni);
(D) removing the template to leave only a metal catalyst skeleton having a reverse opal structure, and having a reverse opal structure for a polymer electrolyte fuel cell (PEMFC). A method for producing a metal catalyst electrode.   2. The template according to claim 1, wherein in the step (b), the template made of colloidal crystals is formed on the gas diffusion layer by evaporation of a polymer colloidal suspension and self-assembly by capillary force. Of manufacturing a metal catalyst electrode having an inverted opal structure for a polymer electrolyte fuel cell. The polymer colloidal particles may be polystyrene, polymethyl methacrylate, polyacrylate, poly-α-methylstyrene, polybenzyl methacrylate, polybenzyl methacrylate, or polybenzyl methacrylate.
rylate), polyphenyl methacrylate (polyphenyl methacrylate)
ylate), polydiphenyl methacrylate (polydiphenyl methacrylate)
crylate), polycyclohexylmethacrylate (polycyclohexyl)
methylacrylate), styrene-acrylonitrile copolymer (styrene)
-Acrylonitrile copolymer), or styrene-methyl methacrylate copolymer.
The method for producing a metal catalyst electrode having an inverse opal structure for a polymer electrolyte fuel cell according to claim 2 , comprising:   The method according to claim 1, wherein in the step (c), the metal skeleton is formed by an electrochemical deposition method.   The metal catalyst electrode having an inverse opal structure for a polymer electrolyte fuel cell according to claim 1, wherein, in the step (d), the template is removed by dissolution with an organic solvent or low temperature calcination. Manufacturing method.